Feedback (or “acoustic positive feedback”) occurs when a sound loop exists between an audio input (e.g., a microphone) and an audio output (e.g., a loudspeaker). For example, a signal received by a microphone may be amplified and passed out of a loudspeaker. The sound from the loudspeaker can then be received by the microphone again, amplified further, and then passed out through the loudspeaker again. The frequency of the resulting sound is determined by resonance frequencies in the microphone, amplifier, and loudspeaker, the acoustics of the room, the directional pick-up and emission patterns of the microphone and loudspeaker, and the distance between them. For small public address (PA) systems, the sound of feedback is readily recognized as a loud squeal, screech, or howl.
A conversation between two persons can be difficult in a shared acoustic space where other people are also speaking, where there are other sources of noise (speech and non-speech), and/or where physical limitations of the environment otherwise make speech difficult. For communications between two persons in a shared acoustic space using microphone(s) and loudspeaker(s), feedback can be particularly detrimental.